Ubuntu has a lot of mobile oriented free software in it's mobile phone/tablet images that could be interesting for packaging into Debian.

Libraries / middleware

Various Qt bindings, libraries that are not all in Debian

Applications

Unity 8 is the shell for launching applications, showing indicators, displaying content from scopes, and so on. It depends on many other components like https://launchpad.net/unity-api and https://launchpad.net/unity-scopes-api.

Ubuntu Core Apps includes community developed applications that are in production use also in the sellable Ubuntu phones (not all pre-installed, like Terminal). They are for the most part pure QML with occasional C++ QML module, but depend on the QML module from Ubuntu UI Toolkit.

Most applications in the app store are free software too. Apps are delivered in the Click packaging format on the phones.

Devices running Ubuntu

BQ and Meizu are announced launch partners for commercially sold Ubuntu phones. They released the following devices:

https://wiki.ubuntu.com/Touch/Devices has former or current Canonical supported references devices:

Community supported devices at system-image.ubports.com:

See also the list of tens of working community ports (without a system image server).